1. DO NOW 10/18 WOD: DETER (di TUR) v. to discourage; to keep someone from doing something DO NOW: Please prepare yourselves for a (quick) quiz on water! (SAQ2.6 from your text)

2. INB PG 20 CHAPTER 2.4: PROTEINS

3. PROTEINS Composed of monomers called amino acids Extremely important macromolecule More than 50% dry mass of cell is protein

4. FUNCTIONS OF PROTEINS All enzymes are proteins Essential in cell membranes Hormones (ex: insulin) Hemoglobin Antibodies Structural component (collagen, keratin, etc…) Muscle contraction

5. AMINO ACIDS All amino acids have the same general structure: Central carbon atom bonded to an amine group (-NH2) and a carboxylic acid group (-COOH) Differ in chemical composition of the R group bonded to central carbon

6. AMINO ACIDS 20 diff. amino acids all with diff. R groups Commonly abbreviated as three letters (ex glycine=gly) or by single letter (glycine=G)

7. THE PEPTIDE BOND One amino acid loses a hydroxyl (-OH) group from is carboxylic acid group, while another amino acid loses a hydrogen atom from its amine group This leaves a carbon atom free to bond with a nitrogen atom forming a link called a PEPTIDE BOND

8. PEPTIDE BOND Strong covalent bonds Water is removed (condensation rxn!!) 2 amino acids= dipeptide More than 2= polypeptide A complete protein may contain just one polypeptide chain, or many that interact with each other

9. PEPTIDE BOND In living cells, ribosomes are the sites where amino acids are joined together to from polypeptides This reaction is controlled by enzymes Polypeptides can be broken down (hydrolysis) to amino acids. Happens naturally in stomach and small intestine during digestion

10. PRIMARY STRUCTURE Polypeptide chains may contain several hundred amino acids linked by peptide bonds The particular amino acids and their ORDER in the sequence is called the primary structure of the protein

11. PRIMARY STRUCTURE There are enormous numbers of different primary structures possible A change in a single amino acid in a polypeptide can completely alter the structure and function of the final protein

12. SECONDARY STRUCTURE The particular amino acids in the chain have an effect on each other even if they are not directly next to one another

13. SECONDARY STRUCTURE Polypeptides often coil into a corkscrew shape called an α-helix Forms via hydrogen bonding between the oxygen of the – CO group of one amino acid and the –NH group of an amino acids four places ahead of it Easily broken by high temperatures and pH changes

14. SECONDARY STRUCTURE Hydrogen bonding is also responsible for the formation of β-pleated sheets Easily broken by high temperatures and pH changes

15. SECONDARY STRUCTURE Some proteins show no regular arrangement; depends on which specific R groups are present In diagrams, β-sheets are represented by arrows and α-helices are represented by coils or cylinders. Random coils are ribbons.

16. DO NOW 10/30 WOD: EGG (eg) v. to encourage or incite to action The bully EGGED the little boy to fight until he cried. My friends EGGED me to try out for the tennis team. Without the crowd EGGING me on, I don’t think I could have finished running the marathon. What determines a protein’s primary structure? Secondary structure? 10/31Proteins pt 223 10/31Macromolecule chart24

17. TERTIARY STRUCTURE In many proteins, the secondary structure itself it coiled or folded Shapes may look “random” but are very organized and precise The way in which a protein coils up to form a precise 3D shape is known as its tertiary structure

18. TERTIARY STRUCTURE 4 bonds help hold tertiary structure in place: 1.) Hydrogen bonds : forms between R groups 2.) Disulfide bonds : forms between two cysteine molecules 3.) Ionic bonds : form between R groups containing amine and carboxyl groups 4.) Hydrophobic interactions : occur between R groups which are non-polar (hydrophobic)

19. QUATERNARY STRUCTURE Most protein molecules are made up of two or more polypeptide chains (Ex: hemoglobin) The association of different polypeptide chains is called the quaternary structure of the protein Chains are held together by same types of bonds as tertiary structure

20. GLOBULAR PROTEINS A protein whose molecules curl up into a “ball” shape is known as a globular protein Globular proteins usually play a role in metabolic reactions Their precise structure is key to their function! Ex: enzymes are globular proteins

21. GLOBULAR PROTEINS Globular proteins usually curl up so that their nonpolar (hydrophobic) R groups point into the center of the molecule, away from aqueous surroundings Globular proteins are usually water soluble because water molecules cluster around their outward-pointing hydrophilic R groups

22. HEMOGLOBIN Hemoglobin is the oxygen carrying pigment found in red blood cells, and is a globular protein Made up of four polypeptide chains (has quaternary structure) Each chain known as globin.

23. HEMOGLOBIN Two types of globin used to make hemoglobin: 2 α-globin (make α-chains) 2 β-globin (make β-chains)

24. HEMOGLOBIN Nearly spherical due to tight compaction of polypeptide chains Hydrophobic R groups point toward inside of proteins, hydrophilic R groups point outwards Hydrophobic interactions are ESSENTIAL in holding shape of hemoglobin

25. SICKLE CELL ANEMIA Genetic condition in which one amino acids on the surface of the β-chain, glutamic acid, which is polar, is replaced with valine, which is nonpolar Having a nonpolar (hydrophobic) R group on the outside of hemoglobin make is less soluble, and causes blood cells to be misshapen

26. HEMOGLOBIN Each polypeptide chain of hemoglobin contains a heme (haem) group Important, permanent part of a protein molecule but is NOT made of amino acids Each heme group contains an Fe atom that can bind with one oxygen molecule A complete hemoglobin molecule can therefore carry FOUR oxygen molecules

27. FIBROUS PROTEINS Proteins that form long strands are called fibrous proteins Usually insoluble in water Most fibrous proteins have structural components in cells (ex: keratin and collagen)

28. COLLAGEN Most common protein found in animals (~25% total protein) Insoluble fibrous protein found in skin, tendons, cartilage, bones, teeth, and walls of blood vessels Important structural protein

29. COLLAGEN Consist of three helical polypeptide chains that form a three-stranded “rope” or triple helix Three strands are held together by hydrogen bonds and some covalent bonds

30. COLLAGEN Almost every third amino acid is glycine (very small aa) allowing the strands to lie close and form a tight coil (any other aa would be too large)

31. COLLAGEN Each complete collagen molecule interacts with other collagen molecules running parallel to it These cross-links hold many collagen molecules together side by side, forming fibrils The ends of parallel molecules are staggered to make fibrils stronger Many fibrils together = fibers

32. COLLAGEN

33. Tremendous tensile strength (can withstand large pulling forces without stretching or breaking) and is also flexible Ex: Achilles tendon (almost pure collagen) can withstand a pulling force about ¼ that of steel

34. COLLAGEN Fibers line up in the direction in which they must resist tension. Ex: parallel bundles along the length of Achilles tendon, cross layered in skin to resist multiple directions of force